Chemical vapor deposition is a well-known method for depositing films or coatings on substrates. One known chemical vapor used for depositing a nickel film or coating on a substrate is nickel carbonyl. Typically, the substrates are heated within a deposition chamber to a predetermined suitable reaction temperature, typically 110.degree. C.-180.degree. C. in an atmosphere of nickel carbonyl, Ni(CO).sub.4. The nickel carbonyl reacts at the surface of the heated substrate to deposit the Ni film or coating thereon.
The nickel carbonyl vapor is continuously introduced to the deposition chamber and gaseous reaction byproduct, carbon monoxide, is continuously purged from the deposition chamber in order to maintain proper circulation of reactive nickel carbonyl across the surfaces of the substrates. The substrates may be heated according to well-known methods, such as heat conduction, radiation, inductance and the like.
It is known to manufacture molds or patterns wherein a metal negative of a mold model is prepared by deposition of the metal upon the mold model. The mold model is also known in the art as a mandrel. The mold model/mandrel may be formed of any suitable material such as rubber, metal, plastic, wood and the like. After building up the metal negative to a suitable thickness and strength the metal negative is separated from the mold model/mandrel. Such molds with one or more defining surfaces made from the metal negative are used extensively for the production of thermosetting or thermoplastic articles. The mold either contains or compresses the plastic into the required shape and curing/cooling of the resulting plastic part will retain the shape inherent in the surface of the mold cavity.
An alternative, typical method of manufacturing a mold involves casting a "splash" on a master model and fabricating a production mandrel from the splash. Nickel carbonyl vapor deposition on selected, desired surfaces of the mandrel in a nickel carbonyl vapor deposition chamber provides a nickel shell to which shell is added a backing frame and components to provide, typically, a finished half of the desired mold.
A further alternative method of manufacturing nickel shells known in the art is by the technique of electroforming, wherein nickel is electrolytically deposited on a substrate from a nickel salt solution.
One drawback of electroformed nickel shells and molds, in consequence of the fact that electroformed nickel contains relatively large amounts of sulphur, is that repairs or modifications to the shell or mold by means of welding cannot be performed readily. In contrast, nickel produced by vapor deposition is devoid of sulphur and is, thus, readily weldable.
It is known that both electroformed and vapor deposited nickel can provide mold tool faces with a harder than usual surface for wearability. However, when electroformed nickel is produced with a hard face, it is often done in two steps, viz, a hard skin of nickel alloy, usually nickel/cobalt, is deposited to a nominal thickness in a nickel alloy plating tank; and after the shell is removed from the alloy plating tank, the rear surface is activated to receive an additional nickel deposit and the shell is placed in a pure nickel plating tank to complete the balance of the thickness required. If the activation at the rear of the nickel alloy face is not 100% successful, then a delamination could occur at the interface between the two different hardness layers. This is difficult to inspect and the delamination may occur much later during tool operation. A further problem is that this nickel alloy face can also be very difficult to weld repair if needed.
In contrast, vapor deposited nickel shells are produced in a "one-step" vapor deposition process, wherein a varied nickel hardness is obtained by means of gradually changing the deposition process parameters over the deposition period. This negates the production of distinct layers of nickel subject to delamination.
A further major advantage of the nickel carbonyl vapor deposition process over the electroforming process is that the former can deposit nickel at a rate 5 to 20 times faster than the latter process, which results in a faster and more economical production of nickel shells. Most metal faced molds, used in the production of composite plastics products have several common features which have evolved over the years, namely, a nickel or spray metal face; locating pins or bushings; outer support frame--cast aluminum or fabricated steel; heating/cooling conduit--usually copper tubes located at the rear of the shell; ejector--pin bushings and gates and the like; and a cast backing of, usually, metal filled polymer
Such support frames and backing components as part of the tool backing system are often added to the rear of the shell after the shell is removed from the shell-forming mandrel. This can cause several problems in that the support frame must be mechanically fastened to the rear of the shell and the shell must also be trimmed to size to match the support frame. Both of these steps can induce twists or warps in the shell. Further, since the shell is removed from the mandrel, an alternative method must be found to support the shell during the rear casting technique. Considerable distortion of the shell could otherwise result. Most tool backing systems have an inherent fault in that they are formed of materials that are not matched to the expansion of the metal shell during heat-up and cool down cycle. Most back-up systems have vastly higher thermal expansion characteristics than the metal tool face. This can result in premature failure of the tool due to cracking or delamination. Most backing systems also do not provide an adequate bond between the metal face and the backing material.
Prior art mandrels used with nickel carbonyl vapor deposition processes to produce nickel shells have suffered from several defects. Prior art mandrels are manufactured with a vastly different C.T.E. to nickel. It has been found that it is not advisable to attach metallic components such as metal bushings, sleeves or other fixtures to the mandrel prior to nickel deposition. Generally, such metallic components that are attached to the mandrel will not retain their absolute dimension in location from mandrel to nickel shell because of different thermal expansion characteristics of the mandrel material, metal components and nickel shell. As a result, a metal frame or box that is secured to the rear of a mandrel often distorts the mandrel. Further, it is generally not possible to utilize the mandrel as a support during the fabrication of the nickel shell rear backing after the shell has been formed on the mandrel because the shell must be removed from the mandrel. This is because at room temperature the nickel shell and mandrel have incurred a relative dimensional change. This dimensional change, is in proportion to the degree of thermal expansion difference between the mandrel and the nickel. This dimensional change may result in the nickel shell becoming "locked" on to the mandrel if there is a configuration which is conducive to such an effect, resulting in potential destruction of the mandrel or distortion of the shell after cooling.
Prior art mandrels are also known which are fabricated in the form of thin walled shells of laminated, filled, high temperature epoxy resins which were heated from the rear by an atomized spray of heat transfer fluid such as HTF 500.TM. (ethylene glycol based composition, Union Carbide). The thin walled shell requirement limits the mechanical strength inherent in the mandrels. Such mandrels often cracked or otherwise failed due to thermal stresses, alone, before successful deposition could occur. Further, use of the heat transfer fluid remains a potential source of contamination for the nickel carbonyl vapor deposition process since the presence of a fluid liquid or vapor often spoils a potentially good nickel vapor deposition deposit. In consequence, mandrel structural arrangements have to be subject to precautions to eliminate the chance of any liquid or vapor leaks through any gaskets or seals. It has been found that a major source of contamination was through the mandrel itself by virtue of its porosity to such fluid or vapor. As a result, sealants have to be applied to the rear surface of the mandrel to reduce such leakage. Such sealant application often unfavorably influences the thermal conductivity and does not ensure a leak proof structure.
The prior art considered to be the most relevant to the present invention is as follows. U.S. Pat. No. 3,355,318, issued Nov. 28, 1967--W. C. Jenkin and U.S. Pat. No. 3,158,499 issued Nov. 24, 1964--W. C. Jenkin describes nickel carbonyl deposition onto various non-composite substrates. U.S. Pat. No. 3,784,451 issued Jan. 8, 1974--P. J. Garner describes a metal faced mold with an electroplated spray metal face and a cast backing formed of cement, plaster of Paris or epoxy resin. U.S. Pat. No. 3,175,259 issued Mar. 30, 1965--E. R. Breining et al describes gas deposition using nickel carbonyl to produce molds or dies with the preferred substrate having a matching C.T.E. U.S. Pat. No. 3,111,731 issued Nov. 26, 1963--E. R. Breining et al, describes die construction with gas plating using nickel carbonyl with an internally heated mold having a matched C.T.E. with iron mandrel.